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Coronavirus has swept across the globe, killing thousands of people and leaving thousands more in hospital.

The majority of fatalities have been in older age groups and those with underlying health conditions.

This can mean many think of the virus as something which only seriously effects the elderly.

But the virus doesn't care about your age, and young people are also dying after catching Covid-19.

If you're young, then you are far less likely to die after contracting coronavirus. But some are, and it's their own immune system that is often the cause.

Imperial College London researchers looked at which age groups are most likely end up in hospital with coronavirus. They found that fewer than 5% of under-50s needed to be hospitalised because of their symptoms. The figure rose to 24% for people aged between 70 and 79.

Only 5% of under-40s who ended up in hospital required critical care. But again, this rose to 27% of people in their 60s and 43% of people in their 70s.

Despite the figures, young people have been criticised for acting like they are "invincible" to the virus.

In March, the head of the World Health Organisation, Adhanom Ghebreyesus, issued a stark warning.

He said: "I have a message for young people: you are not invincible, this virus could put you in hospital for weeks or even kill you.

"Even if you don’t get sick the choices you make about where you go could be the difference between life and death for someone else.”

But how is the disease causing the death and hospitalisation of young people? Seemingly fit and healthy people are ending up in hospital after contracting the virus, and a smaller number are dying.

The indiscriminate virus attacks the lungs, in some cases seeing them fill with fluid, leaving people short of breath.

In many cases, people will have more mild symptoms and their own body can fight it off without the need for hospital treatment.

Like any virus, the first line of defence against Covid-19 is our body's own immune system.

When it detects the virus it works to produce antibodies to try and fight it off. In many mild cases, this can be enough to recover.

But in some cases our immune system can act abnormally, and end up being more deadly than the virus itself.

Coronavirus latest

NHS doctor and lecturer Dr Amir Khan said: "Ironically, however, it is the youthful immune system that may become the problem in some people - and this is what was confirmed to have happened in at least some of the cases of young people dying after contracting coronavirus."

More research is now seeing a link between Covid-19 cases and this effect, called the "cytokine storm syndrome" or CSS. The syndrome is where our own immune system doesn't switch off, causing more and more inflammation that can shut down breathing completely.

Cytokines are a type of inflammatory protein used by our immune system.

When our bodies detect the virus, these cells flood to the affected area to help fight the disease.

This causes some local inflammation, which is normal, but in some cases the body goes into overdrive and produces far too much cytokine proteins. This can then cause the body to activate even more immune cells, causing hyperinflammation.

If this inflammation doesn't stop, it can fill the lungs with fluid, causing severe breathing difficulties. This then starts off another reaction, where the fluid attracts bacteria and can cause lungs to fill with pus. This can cause pneumonia, which normally means ending up in hospital.

It can affect people of any age, but scientists say it may explain why healthy young people die from these sorts of conditions.

Dr Khan, senior lecturer at the University of Leeds School of Medicine and the University of Bradford, said : "This fluid then attracts a feeding frenzy from bacteria that are normally kept in check. These now multiply exponentially, and the lungs fill with pus. This causes pneumonia, requiring urgent hospitalisation.

"A prolonged cytokine storm will eventually shut down breathing completely. The airways get clogged and cells no longer properly absorb oxygen."

UK Government health secretary Matt Hancock, who has had cororonavirus, discussed how deadly the body's own immune response can be.

He said: "For some people, the people who often get into the worst of health and those who lose their lives, it’s often because the lungs over-react to the virus, there’s an immune response. And you just don’t know if that’s going to happen, so I found it really worrying.”

Although the deadly effects of the virus are now being seen in the UK, the link between fatalities and CSS was seen early on in China.

Age and sex distribution of confirmed coronavirus cases in Wales

Female aged 10 and under: 0.3%

Male aged 10 and under: 0.4%

Female aged 10-19: 0.6%

Male aged 10-19: 0.6%

Female aged 20-29: 6.3%

Male aged 20-29: 3.6%

Female aged 30-39: 8.3%

Male aged 30-39: 4.7%

Female aged 40-49: 11.1%

Male aged 40-49: 6.1%

Female aged 50-59: 11.6%

Male aged 50-59: 6.9%

Female aged 60-69: 5%

Male aged 60-69: 5.2%

Female aged 70-79: 4.6%

Male aged 70-79: 7.7%

Female aged 80-89: 5.3%

Male aged 80-89: 6.6%

Female aged 90-99: 2.6%

Male aged 90-99: 1.5%

A recent study published in the medical journal The Lancet said there was "accumulating evidence" some patients with severe Covid-19 might have had CSS.

University of Alabama professor and expert on immune reaction to infections, Randy Cron, said many of the severely ill coronavirus patients in China appear to have CSS.

"No one knows why some people — and not others — develop this response, but there are likely host risk factors, including genetic mutations in genes that contribute to a familial form of this disease."

Professor Ian Humprhys, infection researcher at Cardiff University, has investigated cytokine storms in flu cases in his lab, and said CSS played a role in the SARS (severe acute respiratory syndrome) outbreak of 2003, which resulted in more than 8,000 cases and 800 deaths.

Mr Humprhys said: “The new coronavirus strain is related to the SARS virus.

"The ‘cytokine storm’ was shown to be a major aspect of the disease caused by SARS. It is therefore very likely that inflammation triggered by this new coronavirus is contributing to the disease.

"I would think that will be particularly the case in patients that succumb to respiratory failure.”

He added that it is “very likely” the inflammation is contributing to the effects of the disease, but questions remain over by how much.